The present invention relates to vibratory feeders and conveyors. Particularly, the invention relates to linear motor drives for differential motion conveyors.
Conventional designs of reciprocating vibratory conveyors usually employ electromagnetic drives, or motor driven mechanical drives. An electromagnetic drive utilizes the oscillating magnetic attraction between a magnet armature and a pole face of a magnet. Practical use of the electromagnetic drive requires that the magnet armature be in relative close proximity to be attracted to the pole face of the magnet, putting a severe limitation on the maximum stroke obtainable, usually under 0.1 inches. The design must operate at higher frequencies, about 30 Hz and higher, in order to achieve the accelerations needed to obtain the desired conveying feed rates. Motor driven mechanical drives typically include rotary motors that spin eccentric weights or turn shafts which are connected to cams or crank arms. Mechanical drives convert rotary motion to linear vibratory motion and produce some form of harmonically varying stroke at a set frequency. Mechanical drives generally operate at strokes up to 1 inch, at frequencies ranging from 8 Hz to 20 Hz.
One type of reciprocating vibratory conveyor is known as a differential motion conveyor. This type of conveyor utilizes a motor driven mechanism containing at least two geared shafts with weights of differing eccentricities on each shaft. The mechanism produces a linear reciprocal horizontal motion of the conveying surface that has a lower acceleration and velocity in the forward direction than in its rearward direction. This difference in acceleration and velocity allows the product being conveyed to slip less in the forward direction than when the conveying surface is accelerating in its rearward direction, thus the product moves forward along the conveying surface. Differential motion conveyors are manufactured for example by FMC Corporation""s Material Handling Equipment Division of Homer City, Pa.
There exists prior art in which some form of an electromagnetic linear motor is used as a drive mechanism for vibratory feeders and conveyors. Examples of linear motors are disclosed in U.S. Pat. No. 4,371,800 assigned to ICAL, U.S. Pat. No. 4,921,090 assigned to FMC Corporation, and U.S. Pat. No. 5,409,101, assigned to Allen Fruit Company.
There are three general types of electromagnetic linear motors. A voice coil actuator uses a coil located in a magnetic field which exerts a force on the coil when a current is conducted through the coil. A voice coil actuator is typically used in audio speakers and disk drive positioners. An induction motor uses a stator having coils and an armature made of magnetic material. Induction of currents generated in the armature creates magnetic fields which are either attracted or repulsed by magnetic fields generated by the stator coils. Induction motors are typically used as motors for trains and monorails. A moving magnet motor uses a stator with a plurality of coils which are sequentially energized by a control. An armature carrying permanent magnets is moved in relation to the stator by the energized coils. Moving magnet motors have been used for precision positioning applications.
The present inventors have recognized that it would be advantageous to produce an electromagnetic, linear-motor-driven differential motion conveyor which is not large and complex, and which contains a minimum amount of small components that otherwise make the conveyor difficult to assemble and set up. The present inventors have recognized that it would be advantageous to produce a linear motor drive for a differential motion conveyor which is capable of producing the power or stroke required for an effective and efficient conveyor.
A differential motion conveyor or feeder is contemplated which includes: a base; a trough supported from the base, and a cylindrical linear motor having an armature and an annular stator surrounding the armature. In the preferred arrangement, the stator includes a series of coils spaced along a length of the stator, and the armature includes a series of magnets spaced along a length of the armature. Other cylindrical electromagnetic linear motors are also encompassed by the invention, such as for example, a stator having magnets and an armature having coils. One of the annular stator or the armature is operatively connected to the trough for driving the trough into reciprocation.
In one variation of the invention, the differential motion conveyor or feeder can advantageously have the stator rigidly, operatively connected to a rigid base and the armature rigidly, operatively connected to the trough. The trough can be supported from the base on springs.
In another variation of the invention, the trough is supported from the base on leaf springs, the stator is rigidly, operatively connected to the base, the armature is rigidly, operatively connected to the trough, and the base is supported on base springs.
In a further variation of the invention, the trough is supported from the base on leaf springs, the stator is rigidly, operatively connected to the base, the base is supported on base springs, and the armature is rigidly, operatively connected to a counterweight or block.
In a still further variation of the invention, the trough is supported from the base by support springs, and the stator is rigidly, operatively connected to the base and the armature is operatively connected to the trough by a xe2x80x9csoft startxe2x80x9d trough spring. The base is supported on pedestals or base springs depending on the mode of operation of the conveyor.
The present invention makes the use of linear motor technology practical for vibratory feeder and conveyor applications, by minimizing the number of component parts, by enhancing overall size reduction, by providing a rugged industrial construction, all by contemplating the use of a cylindrical moving magnet linear motor, originally utilized for precision linear positioning applications.
Whereas some conventional motors for differential motion conveyors are limited in stroke length and operational flexibility, the moving magnet linear motor of the present invention may have strokes of 1xe2x80x3 to 12xe2x80x3 and even longer depending on its design and geometry. The linear motor may be operated at various displacement speeds, and made to reciprocate about a point at different speeds in one direction than in the opposite direction. The linear motor may be operated to reverse the speed direction if required. Whereas mechanical type, motor driven vibratory mechanisms require secondary mechanisms to produce linear vibratory motion, the linear motor eliminates the secondary mechanisms such as belts, pulleys, shafts etc., and is not limited to producing harmonic velocity patterns of motion. The linear motor eliminates the need for large complex mechanisms used to drive mechanical differential motion conveyors and can readily be adapted to produce the differential velocities and accelerations required for conveying material.
The linear motor eliminates the need for the gears, shafts and eccentric weights of the prior art mechanical drives. The disclosed invention solves the problems of prior attempts at linear motor drives for differential motion conveyors through the use of a cylindrical moving magnet linear motor that is compact in size, being about the size of conventional AC voltage rotary motors. The linear motor has a rugged, enclosed industrial design. The linear motor has a flexible geometry that allows easy adaptation to various configurations of vibratory feeders and conveyors.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.